The present invention relates to a multi-wall sack.
The present invention relates particularly to a multi-wall sack which comprises an outer bag, typically formed from paper, and an inner pouch, typically formed from a polymeric material.
The present invention relates more particularly although by no means exclusively, to a multi-wall sack of the type described in the preceding paragraph which is suitable for storing dry food products, such as powdered milk products.
A known multi-wall paper/polymeric material sack for dry food products comprises an inner polyethylene pouch and an outer paper bag having a block (ie rectangular bottom end.
The block bottom end provides a flat closed base for the sack and is formed by folding the outer paper bag (and not the inner polyethylene bag) in a specific manner during manufacture of the sack. The arrangement is such that when the sack is filled through the opposite open end, the dry food products in the inner polyethylene pouch push against the folded closed end and cause it to flatten out to create the block bottom end.
After the sack has been filled, the open end of the polyethylene pouch is closed by pressing together the polyethylene material along a line spaced a short distance from the end of the sack and heat sealing together the polyethylene material along the line.
Thereafter, the open end sections of the paper outer bag that are on opposite sides of the heat seal line are pressed together and then folded back and adhered together to form a pinched top end of the sack.
In terms of overall shape, the above-described known sack is wedged-shaped, with the front and rear sides converging from the block bottom end to the pinched top end.
Whilst the known sack has acceptable properties from the viewpoint of long-term storing dry food products, a disadvantage of the sack is that the wedge-shape is not ideal for stacking on pallets. This is a disadvantage because it affects the transportation of filled sacks to an end location. In many situations, particularly export oriented industries, this can be a serious disadvantage.
An object of the present invention is to provide a multi-wall sack which is not subject to the disadvantage described in the preceding paragraph to the same extent as the known multi-wall sack.
According to the present invention there is provided a multi-wall sack containing a product, which sack comprises:
(a) an inner pouch that is filled with product and sealed;
(b) an outer bag that encloses the sealed inner pouch and comprises a block bottom end and a block top end.
According to the present invention there is also provided a multi-wall sack which comprises:
(a) an inner pouch that is adapted to be filled with product and sealed; and
(b) an outer bag that is manufactured with a block bottom end and is adapted to be closed, after the inner pouch has been filled with product and closed, to form a block top end.
The above-described filled sack has a substantially uniform depth along the length of the sack and therefore can be stacked effectively and efficiently on a pallet.
The inner pouch and the outer bag may be formed from any suitable material.
It is preferred that the inner pouch be formed from a polymeric material.
It is preferred that the outer bag be formed from paper.
It is preferred particularly that the outer bag comprise a plurality of layers of paper.
It is preferred that the outer bag contains an easy open device that facilitates removal of the inner bag.
According to the present invention there is also provided a method of forming a closed multi-wall sack having an inner bag and an outer bag which encloses the inner bag and has block ends, the method comprising the following steps at the completion of filling a product into the sack through an open end of the sack:
(i) sealing the product in the inner bag;
(ii) opening out the sides of the outer bag at the open end of the sack to form outturned side flaps and inturned triangular wings;
(iii) folding inwardly an outer section of one of the flaps onto the inner section of the flap;
(iv) folding inwardly an outer section of the other flap onto the inner section of the flap and to overlap partially the folded flap so that the outer bag forms a block end; and
(v) adhering or otherwise holding together the block end.
It is preferred that step (i) comprises sealing the product in the inner bag by pressing together the inner bag along a line extending across a section of the inner bag in the region of the open end of the sack and heat sealing the inner bag along the line.
It is preferred particularly that, after step (i) and before the step (ii), the method comprises trimming the length of the sack above the seal line.
It is preferred that step (v) comprises adhering a cover label over the folded block end.
The label may or may not contain an easy-open device.